(a) Technical Field
The present invention relates to a motor driven brake system. More particularly, the present invention relates to a motor driven brake system including a parking brake.
(b) Background Art
A motor driven brake system refers to a next-generation brake system which is able to provide a faster and more precise braking response performance as compared with an existing hydraulic brake system, a more simplified package layout due to removal of hydraulic pipe lines, minimal environment pollution without using brake oil, simple development of efficient application logic, improved collision safety due to removal of a master cylinder and a vacuum booster, and the like.
In a motor driven brake system a brake pad is pressed by converting rotary power transmitted from a motor and a decelerator into linear power using a screw like mechanism. As a result, the motor driven parking brake system obtains braking power. On the contrary, when power is off, the screw like mechanism is unscrewed in the reverse direction by the pressing force of the brake pad, so that the braking power is released.
Because of these features of the motor driven brake system, a separate parking brake apparatus may be combined with the motor driven brake system so that parking braking power can be provided when the power is off. That is, since a separate parking brake in the existing hydraulic brake system more expensive and heavy, a separate parking brake apparatus configured to share motor power for braking with the motor driven brake system may be mounted to the motor driven brake system in an effort to solve these problems.
Hereinafter, the configuration and operation of a conventional motor driven brake system having a parking brake will be described with reference to FIGS. 1 and 2.
In FIGS. 1 and 2, reference numeral 100 represents a motor driven brake system, and reference numeral 200 represents a parking brake. The motor driven brake system 100 includes friction pads 104 attached in a caliper housing 102, and a disk 106 disposed between the friction pads 104 so as to be pressed by the friction pads 104. A piston 108 movable forward and backward is installed in a horizontal through aperture of a caliper housing 102, and a pressure member 110 having a screw aperture is integrally installed inside the piston 108.
In this case, a reduction gear and an electric motor 114 having both side shafts are mounted at an inner end portion of the caliper housing 102. Here, an outside shaft of the electric motor 114 is connected by means of the reduction gear to a screw-shaped push rod 116 inserted and fastened into the screw aperture 112 of the pressure member 110, and an inside shaft is employed as a rotating shaft 120 having a locking pin 118 formed on the outer circumferential surface thereof.
Meanwhile, as one configuration of the parking brake 200, a parking brake housing 202 is integrally mounted to an inner surface of the electric motor 114, and the rotating shaft 120 of the electric motor 114 is rotatably disposed at a central portion of the parking brake housing 202.
A solenoid 204 is mounted on the inner surface of the parking brake housing 202, and a horizontal pipe 206 is disposed between the solenoid 204 and the rotating shaft 120. A sliding disk 208 in the shape of a vertical plate is integrally formed with the inner end portion of the horizontal pipe 206. In this case, as shown in the sectional view taken along line D-D of FIG. 2, a locking groove 212 into which the locking pin 118 of the rotating shaft 120 is inserted is formed in the inside diameter surface of the horizontal pipe 206.
A spring 210 is disposed between the solenoid 204 and the sliding disk 208 to be compressible and expendable. A friction plate 214 that the sliding disk 208 frictionally contacts to perform parking braking is attached to the inner wall surface of the parking brake housing 202.
A controller 220 for turning on/off the power supplied to the device is connected to the electric motor 114 and the solenoid 204. Thus, during normal braking, the controller 220 turns on the electric motor 114 and simultaneously turns on the solenoid according to a degree to which a brake pedal is pushed.
Subsequently, when the push rod 116 of the electric motor 114 performs a standing rotation, the pressure member 110 fastened to the push rod 116 performs a rectilinear motion toward a vehicle outer direction. This is because the push rod 116 is formed in a screw like shape.
Continuously, the piston 108 integrally formed with the pressure member 110 presses the friction pads 104, and simultaneously, the disk 106 interposed between the friction pads 104 is pressed, so that braking is performed during driving. In this case, as power is applied to the solenoid 204, the parking brake is released.
That is, when the solenoid 204 is turned on, the solenoid 204 pulls the sliding disk 208 by means of the force from an electromagnet. In this case, the sliding disk 208 is spaced apart from the friction plate 214, so that the parking brake is released the rotating shaft 120 of the electric motor 114 becomes rotatable. Simultaneously, the spring 210 disposed between the solenoid 204 and the sliding disk 208 is compressed.
Accordingly, the forward/reverse rotation of the push rod 116 on the same axle with the rotating shaft 120 of the electric motor 114 is restricted, so that the braking operation of the motor driven brake system during driving can be smoothly performed together with the releasing of the parking brake.
On the other hand, when power to the solenoid 204 is turned off after the motor driven brake system is operated, the sliding disk 208 is adhered closely to the friction plate 214 while being slid by the resilience of the spring 210, so that the rotation of the rotating shaft 120 of the electric motor 114 is restricted, thereby operating the parking brake.
That is, the locking pin 118 formed on the rotating shaft 120 of the electric motor 114 is stuck in the locking groove 212 in the horizontal pipe 206 integrally formed with the sliding disk 208 in the state in which the sliding disk 208 is adhered closely to the friction plate 214, so that the rotating shaft 120 of the electric motor 114 is not rotated, thereby operating the parking brake. Accordingly, the reverse rotation of the push rod 116 on the same axle with the rotating shaft 120 of the electric motor 114 is restricted, so that the braking power of the parking brake is maintained.
However, in the conventional motor driven brake system having the parking brake, the operating noise of the solenoid is increased during operation and releasing of the parking brake. Although the braking power should be released for the purpose of safety when the supply of power to the solenoid is stopped while driving, the braking power cannot be released once a power failure occurs. Therefore, the vehicle may lose control, possibly causing a fatal accident.
In other words, when power is not supplied to the solenoid due to an error or failure in the controller when the motor driven brake system is operated during driving of the vehicle when the parking brake is released, i.e., when the power is applied to the solenoid to be turned on, the parking brake is operated as described above, and therefore, the braking power of the motor driven brake system may not be released. Accordingly, the vehicle may lose control thereby causing an accident.